A run of hot-weather days could be turned on their head come Christmas day, as a cool change looks to hit the capital mid-festivities, weather forecasters are predicting.

While the temperatures will almost definitely continue climbing right up until Christmas Eve, the Bureau of Meteorology's Sean Carson said Christmas Day is proving to be the hardest day to predict at the moment. A cool change looks as though it will come through, but forecasters won't be able to put a time on it until much closer to the day.

"At this stage a change is due on Christmas Day. We're probably likely to see a couple of showers and thunderstorms on Christmas Day," Mr Carson said.

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Before the cool relief, the capital is set to reach at least 36 degrees by Christmas Eve, a forecast which Mr Carson said was "conservative", as the mass of hot air that brought soaring temperatures to Australia's south east in late November returns.

"This hot air is associated with the same heatwave we had a few weeks ago," Mr Carson said. "It really hasn't gone very far."

After a sunny top of 29 degrees today, the capital is tipped to hit 33 degrees on Thursday, before dropping back down to 28 degrees on Friday, and then shuffling back up to be 36 degrees by Monday.

For Canberrans heading to the south coast, Mr Carson said there would be a bigger concern than the heat, as the tropical cyclone currently lashing Fiji sends high energy swells towards the east coast of Australia.

Mr Carson said strong swells were expected to arrive at South Coast beaches by Thursday, and presented particular dangers to rock fisherman, and inexperienced swimmers taking holidays along the coast.

The waves would likely come through in "rogue" sets, meaning a calm-looking sea could quickly turn dangerous as powerful waves suddenly swept through.

"It's the worst time of year to get a swell from a cyclone, during the holiday season," Mr Carson said. "It's very inconsistent, but has a lot of energy.'

Mr Carson said in terms of temperature, the South Coast had a higher chance of a mild Christmas day, with any southerly change likely affecting those on the coast first.

This December has already proven significantly warmer than last year, as Canberra prepares for a return to hot summers.

"We've had six days above 30 degrees this December, last December we had zero - so we're well ahead of last year," Mr Carson said.

And with the warm air mass likely to remain over the central parts of Australia, Mr Carson said we can expect plenty more hot days ahead.